The technical field of this invention is radiology and, in particular, bone absorptiometry by radiographic measurements.
The depletion of bone mineral content, typically referred to as osteoporosis, is a common consequence of a variety of diseases and natural aging processes. In addition to metabolic bone diseases and aging, bone minerals can be lost as the result of drugs, stress, dietary deficiencies, pregnancy or lactation. When skeletal bone mass drops below the level necessary to provide mechanical support, the depletion of bone mineral content becomes an important cause of morbidity, particularly in elderly patients.
Unfortunately, at present there are no reliable and inexpensive systems for gauging bone mineral content (BMC) with any high degree of precision, particularly during the early stages of osteoporosis or other mineral depletion disorders when dietary supplements and therapeutic agents may reverse the course of demineralization and prevent debilitating fractures or otherwise slow the progress of the disease.
Conventional methods for determining bone mineral content typically involve measurements of radiation absorption in the bone. U.S. Pat. No. 3,715,588 issued to Rose on Feb. 6, 1973, is illustrative of a prior art "bone scanner" in which a collimated X-ray beam is passed through a bone (e.g., the wrist) and detected by a radiation detector mechanically coupled to the X-ray source. The system scans back and forth across the bone to produce a complete measurement of the bone and surrounding tissue. Because of inherent differences in tissue and bone absorption, bone density (and, hence, mineral content) can be inferred from a logarithmic ratio of the intensity of radiation detected after transmission through the two media.
One problem with bone absorptiometry systems often lies in the inability of the apparatus to physically constrain the patient's limb efficiently for good spatial resolution of the bone and accurate repositioning. Another problem can arise when the limb clamping mechanism leave gaps around the limb, such that absorption irregularities are introduced. Yet, another problem lies in the difficulty in determining the thickness of the limb section insofar as the thickness may vary with the patient's age and current health.
Moreover, additional errors in bone mineral constant measurements can be caused by changes in the energy of the radiation source during operation and from one measurement to the next (or if measurements are taken with different machines). Furthermore, these problems can be compounded by variations in the fat content of a patient's soft tissue over time.
These defects often lead to BMC errors on the order of five percent or more for individual patients, precluding effective use of radiographic imaging techniques for monitoring progressive changes in bone mineral content.
There exists a need for more precise bone absorptiometry systems that can be used by the general medical community. In particular, there exists a long-felt need in the field for better limb positioning and calibration systems for radiographic imaging.